Associating embedded data with an electronic image has been used for many applications. For example, spatial-dependent metadata has been used to associate printing hints with an image. The use of printing hints increases the printer's ability to generate high quality document images. Embedded data has also been used to associate digital rights management information, such as copyright notices and permissions, with a document. However, when an electronic image is edited, the embedded data needs to be modified too, i.e., the embedded data needs to be re-associated with the corresponding edited portion.
One method of editing an electronic image permits the corresponding printing hints to be regenerated and then added; however, this method may be time consuming. Some commercial software image editing tools offer customers many options and choices, such as cropping, scaling, color manipulation and filtering. However, most commercial packages, such as Adobe PhotoShop, do not preserve printing hints. If an editing tool does not preserve printing hints, the edited image must have the printing hints re-associated with the edited image. Similarly, if other embedded data, such as digital rights data, is associated with different portions of an image, after image editing, the digital rights management data must be re-associated with the edited image.
Digital watermark technology has been used in various applications to embed additional information in an electronic image. Digital watermarks are usually printed as marks which cannot be easily identified by the human eye. Digital watermarks have been used to embed and store data associated with an image. Watermarks have also been used to detect edits to electronic images. Typically, “fragile” digital watermarks, which are sensitive to editing, are embedded in the images to be protected. To detect image editing, the watermarks are extracted from the image to be tested and compared to the original watermarks. The image is considered to be altered if significant discrepancies in the watermarks exist. If only a part of the image has been modified, digital watermark technologies may also identify the altered image regions. Nevertheless, the regions are typically detected at a very low-resolution.
There is a need for a method of editing an image which preserves image quality, and which permits embedded data associated with the original image to be easily associated with the edited image. Also, with the advent of image editing software, the ability to manipulate or otherwise alter a digital image is readily available. There is a need to be able to authenticate a digital image in order to determine whether or not the digital image has in fact been altered in some way.